Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2002-12-31
2004-12-28
Vo, Hieu T. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C701S102000, C701S115000, C060S274000, C060S285000, C073S117020
Reexamination Certificate
active
06836722
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rear oxygen sensor of a vehicle, and more particularly, to a method and a system for diagnosing the failure of a first oxygen sensor using a second oxygen sensor.
BACKGROUND OF THE INVENTION
OBD-II, which is an updated On-Board Diagnostic standard effective in cars sold in the United States after 1996, requires a diagnosing device for emissions treating systems that are related to tailpipe emissions and evaporative emissions, and also requires a device for diagnosing a malfunction of such a diagnosing device. A car having an OBD-II system is generally provided with two oxygen sensors (dual oxygen sensor system) to detect oxygen content in exhaust gas. The dual oxygen sensor system comprises a front oxygen sensor, which is located between an engine and a catalytic converter, that is, upstream of the catalytic converter, and a rear oxygen sensor located downstream of the catalytic converter.
If the oxygen sensor does not operate normally, precise air/fuel ratio control cannot be performed and noxious emissions increase. Therefore, in order to meet emission regulations, it is necessary to diagnose a failure of the oxygen sensor. In particular, an electronic engine control unit determines whether or not the catalytic converter operates normally based on signals from the rear oxygen sensor. So diagnosing a failure of the rear oxygen sensor is important in reducing exhaust emissions.
SUMMARY OF THE INVENTION
In a preferred embodiment of the present invention, a method for diagnosing a failure of a rear oxygen sensor of a vehicle comprises: determining whether a predetermined monitoring condition exists; determining whether a vehicle speed is 0; determining whether a difference between a maximum value and a minimum value of monitored signals of the rear oxygen sensor is less than a first value; determining whether the difference is between the first value and a second value, the second value being greater than the first value, if the difference is not less than the first value; injecting fuel for a predetermined period such that an air/fuel ratio becomes a predetermined air/fuel ratio, the predetermined air/fuel ratio being richer than a stoichiometric air/fuel ratio, if the difference is between the first value and the second value; detecting an output value of the front oxygen sensor and an output value of the rear oxygen sensor after injecting fuel for the predetermined period; and determining whether the detected output value of the front oxygen sensor is greater than a first threshold value, wherein a front air/fuel mixture is determined to be rich if an output value of the front oxygen sensor is greater than the first threshold value, and the detected output value of the rear oxygen sensor is less than a second threshold value, and wherein a rear air/fuel mixture is determined to be rich if an output value of the rear oxygen sensor is greater than the second threshold value.
It is preferable that the method further comprises generating a fault diagnosis signal if the difference between the maximum value and the minimum value of the rear oxygen sensor is less than the first value.
It is further preferable that the method further comprises generating a fault diagnosis signal if the detected output value of the front oxygen sensor is greater than the first threshold value, and the detected output value of the rear oxygen sensor is less than the second threshold value. Preferably, the first value is 0.078V. It is preferable that the second value is a minimum difference between a maximum output value and a minimum output value of the rear oxygen sensor for a diagnosis of a catalytic converter, and the minimum difference is preferably 0.3V. It is preferable that the predetermined air/fuel ratio is 0.85 of lambda, the first threshold value is 0.5V, and the second threshold value is 0.45V.
Preferably, if fuel is reduced by a fully-closed throttle, or by a predetermined map table according to engine load and the halt is maintained for a predetermined reduced period after a vehicle has run for a predetermined run period in a condition that: (1) an engine speed is higher than a predetermined speed, (2) a volumetric efficiency is greater than a predetermined efficiency, and (3) a vehicle speed is greater than a predetermined speed, it is determined that the predetermined monitoring condition exists.
In another preferred embodiment of the present invention, a system for diagnosing a failure of a rear oxygen sensor of a vehicle comprises: a vehicle speed sensor, an engine speed sensor, an air flow sensor, a throttle position sensor, a front oxygen sensor, a rear oxygen sensor, a control unit, and a fuel injector. The vehicle speed sensor generates a signal responsive to a vehicle speed. The engine speed sensor generates a signal responsive to an engine speed. The air flow sensor generates a signal responsive to an air flow rate. The throttle position sensor generates a signal responsive to a throttle position. The front oxygen sensor and a rear oxygen sensor generate signals responsive to an oxygen content in exhaust emission, the front and rear oxygen sensor being disposed upstream and downstream respectively of a catalytic converter. The control unit diagnoses a failure of the rear oxygen sensor, and the fuel injector injects fuel according to an injection command signal of the control unit. In this embodiment, the control unit is programmed to execute an embodiment of the diagnosis method as summarized previously.
An additional preferred embodiment of the method for diagnosing a failed oxygen sensor comprises adjusting an engine fuel/air ratio so that the engine produces a corresponding adjusted exhaust; detecting a first oxygen content of the adjusted exhaust with a first oxygen sensor; detecting a second oxygen content of the adjusted exhaust with a second oxygen sensor; comparing the first oxygen content to a first threshold; comparing the second oxygen content to a second threshold; and concluding that the second oxygen sensor has failed if the first oxygen content is above the first threshold and the second oxygen content is below the second threshold.
REFERENCES:
patent: 5020499 (1991-06-01), Kojima et al.
patent: 5533332 (1996-07-01), Uchikawa
patent: 5758491 (1998-06-01), Agustin et al.
patent: 5927260 (1999-07-01), Kishimoto et al.
patent: 6644017 (2003-11-01), Takahashi et al.
patent: 6718754 (2004-04-01), Kobayashi et al.
patent: 69705150 (2002-03-01), None
patent: 2003-90251 (2003-03-01), None
Hyundai Motor Company
Morgan & Lewis & Bockius, LLP
Vo Hieu T.
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